Distribution and some biochemical properties of rat paraoxonase activity

The calcium-dependent enzyme activity which hydrolyzes the p-nitrophenyl-O-P bond of paraoxon (paraoxonase) has been studied in several rat and human tissues. Rat plasma and liver showed the highest activities (1.31 +/- 0.19, 0.82 +/- 0.09 nmol/min mg protein +/- SEM, respectively), while other tissues showed less than 2% plasma activity. The Arrhenius plot showed monophasic patterns in both tissues with activation energy values of Ea = 57 +/- 3 and 69 +/- 4 kcal/mol degree K for rat liver and plasma, respectively. Rat plasma and liver paraoxonase lost about 80% activity after 24-hr storage at 27-30 degrees C and was not restored by calcium addition. There was no loss of activity in human serum after 3 days and only 33% after 5 days. The pH optimum for paraoxonase activities was about 7.4 for both rat tissues. It is concluded that plasma paraoxonase is similar to the liver enzyme and is a good mirror for total body detoxifying activity.

Soluble and particulate forms of the organophosphorus neuropathy target esterase in hen sciatic nerve

Neuropathy target esterase (NTE) is the suggested "target" molecule involved in the initiation of organophosphorus-induced delayed polyneuropathy. Sciatic nerve NTE was separated into particulate (P-NTE) and soluble (S-NTE) fractions by ultracentrifugation at 100,000 g for 1 h in 0.32 M sucrose and compared with the corresponding brain extract. Total sciatic NTE activity was 80-100 nmol/min/g tissue from which 50-60% was recovered in the soluble supernatant fraction and the remaining 40-50% in the pellet fraction. About 90% of brain tissue activity (approximately 1,800 nmol/min/g tissue) was recovered as P-NTE. A similar distribution was obtained when more drastic centrifugation without sucrose was performed. P-NTE and S-NTE were distributed with the membrane and cytosolic markers assayed, respectively, glucose-6-phosphatase, Na+,K(+)-ATPase, 5'-nucleotidase, phospholipids, and lactate dehydrogenase. When the pH during the centrifugation was increased from 6.4 to 11, recovered P-NTE activity decreased from 1,750 to 118 nmol/min/g tissue for brain and from 31 to 12 nmol/min/g for sciatic nerve. However, S-NTE activity and total nonfractionated control activity were only slightly affected by the same pH treatment. The distribution pattern encountered may be better understood as representing two different proteins than an equilibrium between soluble and membrane-bound portions of a single protein, with P-NTE activity depending on a membrane factor from which it is separated through fractionation at high pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical and clinical tests of the delayed neuropathic potential of some O-alkyl O-dichlorophenyl phosphoramidate analogues of methamidophos (O,S-dimethyl phosphorothioamidate)

The interaction in vivo of four O-alkyl O-2,5-dichlorophenyl phosphoramidates with neural neuropathy target esterase (NTE) and acetylcholinesterase (AChE) and their ability to cause delayed polyneuropathy in hens has been examined. Previous studies in vitro (Vilanova, Johnson & Vicedo, Pestic. Biochem. Physiol., 28 (1987) 224) had led to the prediction that these compounds would not be neuropathic but, rather, would be prophylactic agents against organophosphorus-induced delayed polyneuropathy. In vivo the effects of these esters on the enzymes differ in 2 respects from effects in vitro: (i) Relative sensitivity of the enzymes was different: thus greater than 50% of brain NTE remained 24 h after an oral dose of 15 mg/kg of the n-hexyl ester while only 10-30% of AChE remained although NTE was the more sensitive enzyme in vitro; (ii) In no case could the inhibited NTE or AChE in autopsy samples from birds dosed with any of the 4 esters be reactivated by treatment with potassium fluoride in vitro: the inhibited enzymes produced by incubation of tissue with the esters in vitro had been reactivatable. Prophylaxis, with therapy in some cases, was required to prevent acute anticholinesterase poisoning when doses were sufficient to cause high inhibition of neural NTE. Inhibition in brain was typically 5-10% more than in spinal cord and 10-15% more than in sciatic nerve. Unambiguous signs of polyneuropathy (Grade 3 or more on an 8-point scale) were not seen in birds observed up to 3 weeks after doses which caused less than 70% inhibition of NTE in brain and spinal cord or less than 60% inhibition in sciatic nerve of pair-dosed birds assayed 24 h after dosing. Doses of 300, 10, 100 and 65 mg/kg, respectively, of the methyl, ethyl, n-butyl and n-hexyl esters caused greater than 70% inhibition of NTE in all 3 neural tissues and neuropathy in the majority of observed birds. Analysis of consolidated dose/response data from 36 assayed and 51 observed birds showed that effects of Grade 3 or more were produced in about 90% of birds when inhibition of NTE was greater than 90% in brain, greater than 85% in spinal cord or greater than 75% in sciatic nerve.(ABSTRACT TRUNCATED AT 400 WORDS)

Sciatic nerve neuropathy target esterase. Methods of assay, proximo-distal distribution and regeneration

Some organophosphorus compounds (OP) induce a delayed polyneuropathy (OPIDP) which is initiated by the phosphorylation of the so-called neuropathy target esterase (NTE). In this work some aspects of hen sciatic nerve NTE are studied. The assay method is reported and modifications are discussed and a combined method proposed. Proximo-distal distribution showed a significant difference from proximal (100 +/- 10%) to distal (69 +/- 9%) fragments, in accordance with reported data. The time course of in vivo regeneration after a single TOCP dose (200 mg/kg, post oral) showed some differences when compared with hen brain NTE. Sciatic nerve NTE showed a delay of 2-3 days before regeneration but then regenerated faster (74% activity at day 7) than brain NTE (50% activity at day 7). A slower rate of regeneration of distal than proximal segments has been suggested to explain higher sensitivity of distal segments [3], however in this work no significant differences were observed in the rate of regeneration when comparing proximal and distal fragments.

Low non-neuropathic tri-o-cresyl phosphate (TOCP) doses inhibit neuropathy target esterase near the neuropathic threshold in n-hexane pretreated hens

Simultaneous intoxication with hexacarbon solvents and organophosphorus compounds has been considered a possible critical factor in some occupational neuropathies and their interactions proved to cause potentiation effects in hens [1-3]. A high degree of inhibition of neuropathy target esterase (NTE) is needed to develop organophosphorus induced polyneuropathy (OPIDP). In this work, the inhibition of NTE, BuChE and AChE by TOCP on control and n-hexane pretreated (7-15 days, 300 mg/kg per day) hens is studied. Using a single TOCP dose of 200 mg/kg, n-hexane pretreated hens showed synergistic effects, but no significant differences were observed in the inhibition of cholinesterases and NTE in brain or spinal cord. With lower TOCP dose (20 mg/kg) statistically significant differences were observed, which were not drastic but could be important because they involved an increase of inhibition up to critical threshold values (from 40-50% to 60-70% inhibition). However, no clinical effects were observed in these animals. Possible mechanisms of neurotoxic interaction are discussed.

Tuberculous panophthalmitis associated with drug abuse

Tuberculous endophthalmitis is a rare condition not described to date in association with intravenous drug abuse. Characteristics such as the lack of proven tuberculous disease in other organs and intense progression towards panophthalmitis make this case all the more interesting. The histopathological diagnosis is based on the identification of acid-alcohol resistant bacilli, and typical granuloma lesions with focal caseosis in stained sections.

Sensitivity to tri-o-cresylphosphate neurotoxicity on n-hexane exposed hens as a model of simultaneous hexacarbon solvent and organophosphorus occupational intoxication

Hens were given a single oral dose (0.235 mg/kg) of tri-o-cresylphosphate (TOCP) during chronic n-hexane treatment (200 mg/kg daily, 5 days/week). They were compared with other animals treated only with n-hexane or only with TOCP. Animals treated with a higher TOCP dose (1 ml/kg) were used as positive controls. The animals treated with both n-hexane and TOCP showed rapid development of severe ataxia. The rate of the ataxia development was similar to that of the positive controls but with earlier onset of the first signs and with less loss of body weight. However, animals treated only with n-hexane, under the same conditions, showed only reversible weakness and sedative effects, and those treated only with TOCP showed slow and slight ataxia development. The n-hexane- and TOCP-treated hens showed axonal swelling with myelin retraction associated with Ranvier's nodes, which is characteristic of long hexacarbon exposure. Some internodal swellings were also observed but less frequently than the paranodal swellings. The time course of the ataxia development was similar to an organophosphorus-induced delayed neuropathy (OPIDN); however, the light microscopy observation more closely resembled hexacarbon neuropathy. The results suggest a potentiation effect of n-hexane and TOCP neurotoxicities which could be related to some human occupational neuropathies.

Phthalates and organophosphorus compounds as cholinesterase inhibitors in fractions of industrial hexane impurities

Cholinesterase (ChE) inhibitors have been described in the distillation residue of hexane and other industrial solvents. The residue of a commercial hexane has been fractionated by preparative chromatography. The anticholinesterase (antiChE) activity was isolated in two fractions (F-5, F-7) which contained only 0.61 and 0.16% respectively of the original dry weight hexane residue. In the former fraction, reversible and irreversible progressive inhibition was observed, and organophosphorus compounds (OPs) were detected colorimetrically and by gas chromatography. This fraction was subfractionated in a second chromatographic step. One subfraction containing the highest antiChE activity and 88% phosphorus of F-5 was isolated. In this subfraction triphenylphosphate and other not definitely identified OP compounds were detected by gas chromatography/mass spectrometry, together with several adipates and phthalates, including di-n-butylphthalate. This phthalate could explain the reversible inhibition of ChE by the hexane residue, and triphenylphosphate and the unidentified OP the irreversible inhibition. A possible toxicological role of these impurities is discussed in relation to occupational neuropathies by exposure to solvents.

Serum cholinesterase inhibitors in the commercial hexane impurities

Commercial hexane was concentrated by distillation. The distillation residue (0.43 ml/l original solvent) contains material which inhibits human serum cholinesterase (ChE) "in vitro" with a slight effect on acetylcholinesterase. Phosphorus was detected equivalent to 0.33 mumol monophosphorus compound/litre original solvent. The inhibition was progressive with the enzyme-inhibitor preincubation time. A partial reactivation of the inhibited enzyme was obtained by treatment with hydroxylamine and 2-PAM. The results are coherent with a covalent inactivation by more than one inhibitor which acylate (probably phosphorylate) ChE, although it seems likely that a reversible but unstable inhibitor could also be present in the hexane residue. The results are discussed in the context of the known neurotoxic effects of n-hexane and some organophosphorus esters.